FERTILISERS (GENERAL METHODS) ng (b) Nitric Nitrogen, i gram of the fertiliser is treated with 2 c.c. of water, the liquid filtered and the filtrate tested with cone, sulphuric acid and ferrous sulphate in the usual way. (c) Organic Nitrogen. In absence of ammonia, 0-5 gram of the fertiliser is heated with soda lime : evolution of ammonia indicates organic nitrogen. If ammoniacal salts are present, these must be removed by extraction with water and then dried, the insoluble residue being tested with soda lime. 3. Phosphoric Acid. (a) Phosphoric Acid soluble in Water. Half a gram is mixed with 4-5 c.c. of water and left to stand, a little of the clear liquid being pipetted off subse- quently and tested with ammonium molybdate. (b) Soluble in Ammonium Citrate (Retrograde or reverted •phosphate). A few grams are extracted several times with water and the residual insoluble matter digested with about 20 c.c. of ammonium citrate solution (for its preparation, see p. 123) ; the liquid is filtered and the filtrate tested with magnesia mixture. (c) Insoluble. The residue insoluble in ammonium citrate is washed several times with ammonium citrate solution boiled with 7-8 c.c. of nitric acid and allowed to stand, a little of the clear liquid being subsequently tested with ammonium molybdate. 4. Potash. (a) Soluble in Water. About 2 grams are boiled with 10 c.c. of water and the liquid filtered. To one portion of the filtrate an equal volume of 10% sodium thiosul- phate solution is added and then 3-4 drops of Carnot's reagent1 and double the volume of 95% alcohol: in presence of potash a yellow crystalline pre- cipitate is formed. The other portion is rendered faintly alkaline with sodium hydroxide, filtered and acidified slightly with hydrochloric acid. Addition of i c.c. of perchloric acid (D =1-12) and an equal volume of alcohol yields a white precipitate in presence of potash. (b) Insoluble in Water. Two grams are thoroughly exhausted with hot water and the undissolved part boiled with a mixture of 5 c.c. of cone, nitric acid and 10 c.c. of cone, hydrochloric acid, the liquid being diluted, filtered, evaporated to dryness and the residue redissolved in water; this solution is then tested as in the preceding case. 2. Determination of the Moisture From 5 to 10 grams are heated at 100° to constant weight. Superphos- phates and other products rich in gypsum are dried in a boiling water-oven for 4 hours. If the fertiliser has an alkaline reaction or it is feared that ammonia may be lost during the drying, as, for instance, with stable manure, the fertiliser (5 grams) is placed in a tared porcelain boat and this introduced into a glass tube arranged in a suitable oven. One end of the tube is con- 1 100 grams of basic bismuth nitrate (magister of bisrrmth) are dissolved in the hot in cone, hydrochloric acid and diluted to a litre with 92% alcohol., 20-30% as good, 15-20% as ordinary, and less than 15% as poor.